Compressional wave telemetering device



Oct 1953 J. M. JOHNSTON ET AL ,4

COMPRESSIONAL WAVE TELEMETERING DEVICE Filed Oct. 1, 1951 I wad x "M I l ll llllll.

INVENTORi J OJEPH IZ JON/V570 JOSEPH 5- OL 55 HTTOENEYS.

Patented ct. 20, 1953 'COMPRESSIONAL WAVE TELEMETERING DEVICE Joseph M. Johnston, Bradley Beach, N. ,J Joseph B. Olsen, Brooklyn, N. Y., and John A. Moulden,

Red Bank, N. J.

.(Granted :under Title 35, S. :Gode (1952) see. 266) '3 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to us of any royalty thereon.

This invention relates to airborne detection devices and more particularly to a compressional wave telemetering device.

In the past, aneroid barometers and related devices capable of telemetering information to earth have required a plurality of vacuum tubes and equipment for accomplishing the purposes for which they were designed.

The present invention is a device adapted to be sent aloft by balloon for the telemetering of signal back to the earth. The present invention comprises a microphone oscillator transmitter adapted for the telemetering of frequency that changes upon being subjected to a compressional wave.

The objects of the present invention are to provide an improved and simplified telemetering device capable of transmitting a continuous frequency that is altered upon having a compressional wave applied to the device.

The single figure in the accompanying drawing is a side elevation partly broken away and in section of the device that embodies the present invention, together with a fragmentary schematic diagram of the transmitter circuit with which the device is connected.

The device shown in the accompanying drawing comprises a Helmholtz resonator consisting of a hollow aluminum cup I and a Bakelite cover 2 secured together with screws 3. The Helmholtz resonator has a hole 4 in the cup I and preferably a pair of holes 5 and t in a Bakelite plug 7 in the cover 2 of the device. An aluminum diaphragm ID that is sufficiently thin to vibrate has its edge clamped between an upper flanged part of the cup I and the cover 2. The underside of the cover 2 is cut away to accommodate the diaphragm and associated parts.

A microphone is provided for the device in the form of two capacitor plates [2 and I3 mounted in the cut away surface of the cover 2 and in capacitive relationship with each other and with the diaphragm It. The capacitor plates I2 and I3 continue as tubes that are threaded externally for mounting in the cap 2 and internally for the reception of the threaded lower ends of tuned line rods I5 and I6. Lock nuts I! and I8 set the adjustments of the plates I2 and I3 in the cap 2.

The unmounted ends of the tuned line rods I5 and I6 are connected to the grid and plate respectively of an oscillator vacuum tube 20. 3+

platecurrent for the oscillator tube 20 issupplied through a radio frequency .ch-oke coil 2| and the tuned rod Hi to the plate of the tube 20. The grid of the tube 20 is connected through the tuned line rod I5, a radio frequency choke coil 22 and the resistor 23 with the B+ power.

Output from the plate of the tube 20 is trans.- mitted into spacefrom an antenna 25 with which the tube plate is connected. Filament voltage to the tube 2i] is supp ied. through a pair of radio frequency choke coils 30 and 33 shunted on the heater .side by a capacitor 32.. Cathode voltage o th tube 20 is s pplied throu h the radio ire-.- quency choke coil 30 connected in series with a resistor 3|.

The microphone, comprising the cup I and its air volume, the aluminum diaphragm III, the cut-out under face of the Bakelite cap 2, the apertured Bakelite plug 7 and the capacitor plates I2 and I3 that illustratively may be brass disks or the like, is tuned to very low sound frequencies. Since the brass disks or capacitor plates I2 and I3 are in close proximity to the diaphragm In, any change in the position of the membrane or diaphragm II] will cause an electrical capacity change between the disks l2 and I3.

Change in the electrical capacity of the disks I2 and I3 foreshortens or lengthens the tuned lines I5 and I6 of the oscillator and effects the frequency thereof. In the present invention this frequency modulation is accomplished by a single tube and without complex amplifiers and modulators as in comparable previous devices. The microphone disclosed herein can be tuned to respond within a predetermined range of sound frequencies by changing the size of the leak holes 4 and 5 and 6 in the cup I and plug 1 respectively.

In the event the disclosed device is to be modified to be used for obtaining altitude information, a modification, not shown, will comprise a six volt buzzer connected across the filament supply of the oscillator tube 20 and energized from a commutator with a stylus that is moved mechanically as an aneroid cell expands or contracts in response to pressure changes in the ambient atmosphere. The aneroid is ore-calibrated. By counting the buzzes produced as the stylus passes over individual commutator segments altitude determinations may be made.

It is to be understood that the device and the parts thereof that are shown and described herein have been submitted for the purposes of illustrating and explaining an operative embodiment of the present invention and that similarly functioning modifications in the device and its parts may be made wihout departing from the scope of the invention as described herein.

What we claim is:

1. A compressional Wave telemetering device, comprising a microphone oscillator having a microphone comprising a pair of disks capacitively coupled with a diaphragm within a cavity apertured to the outside air on both sides of the diaphragm, a tuned line attached at one end with said pair of disks, an oscillator tube having a transmitting antenna and having a plate grid circuit across which the unattached ends of said tuned line is connected and powered from a B+ power supply.

2. A compressional wave telemetering device, comprising a sound resonator, a diaphragm within said resonator, a pair of disks capacitively coupled with the diaphragm in said resonator, a pair of tuned line rods connected at their first ends with said pair of disks, an oscillator vacuum tube having a plate to which B+ current is supplied through a first radio frequency choke coil and a first tuned line rod and having a grid to which 5+ current is supplied through the second tuned line rod connected through a radio frequency choke coil and a resistor connected in series to the 13+ power supply, a transmitting antenna connected with the plate of said vacuum tube, and a filament voltage supplied to the cathode and filament of said oscillator vacuum tube.

3. A compressional wave sensitive telemetering device, comprising a Helmholtz resonator having two apertures therein opening to the outer air, a diaphragm separating said resonator into two cavities each having an aperture opening tothe outer air, a pair of capacitor plates insulated from each other and coupled in capacitive relation with each other and with said diaphragm, a pair of tuned line rods insulated from each other and connected separately with said pair of capacitor plates, and an oscillator vacuum tube having a plate to which 13+ electric power is supplied through a choke coil and a first tuned line rod and said oscillator vacuum tube having a grid to which B+ electric power is supplied through the second tuned line rod and through a radio frequency choke coil connected in series with a first resistor and to which tube filament voltage is supplied through a pair of radio frequency choke coils shunted by a capacitor with one of said choke coils connected in series with a second resistor to the cathode of said oscillator tube.

JOSEPH M. JOHNSTON. JOSEPH B. OLSEN. JOHN A. MOULDEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,114,036 Smith et al Apr. 12, 1938 23141492 Crawley Aug. 24, 1948 2,451,502 Lisman et a1. Oct. 19, 1948 

